Flame ionization detector assembly

ABSTRACT

A flame ionization detector assembly for use in gas chromatography including a detector and a gas sampling assembly comprising a housing defining primary passage means for gaseous effluent from a chromatography column, a needle and a valve seat, both of which are received in recesses defined by the housing and both of which define passages communicating with the primary passage means whereby a small portion of the gaseous effluent from the chromatography column passes from the primary passage means through the passages defined by the valve seat and the needle to a combustion zone.

United States Patent Guillemin et al.

[ 51 Apr. 25, 1972 [54] FLAME IONIZATION DETECTOR ASSEMBLY [72]inventors: Claude Gulllemln, Paris; Jean-Claude Badln, Bondy, both ofFrance [73] Assignee: Produits Chimique PechineyrSaint-Gobain,

Neuilly-sur-Seine, France [22] Filed: Apr. 6, 1970 [21] Appl. No.:25,759

[30] Foreign Application Priority Data Apr. 11, 1969 France ..691l175'[52] US. Cl. ..23/254 E, 23/232 C, 23/232 E,

23/255 E, 73/23 [51] Int. Cl. ..G0ln 31/00, GOln 31/12,G0ln 27/62 [58]Field of Search ..23/255 E, 254 E, 232 E; 73/23 [56] References CitedUNITED STATES PATENTS 3,215,499 11/1965 Dewaretal. ..23/255 E 1/1966Beroza .....23/230 3,399,974 9/1968 Spencer et al ..23/255 E 3,502,4393/1970 Reece et al ..23/255 E Primary Examiner-Morris 0. Wolk AssistantExaminer-R. E. Serwin Attorney--McDougall, Hersh 8:. Scott ABSTRACT Aflame ionization detector assembly for use in gas chromatographyincluding a detector and a gas sampling assembly comprising a housingdefining primary passage means for gaseous effluent from achromatography column, a needle and a valve seat, both of which arereceived in recesses defined by the housing and both of which definepassages communicating with the primary passage means whereby a smallportion of the gaseous effluent from the chromatography column passesfrom the primary passage means through the passages defined by the valveseat and the needle to a combustion zone.

15 Claims, 1 Drawing Figure i Patented April 25, 1972 1 Gas Y B flv a A5 FLAME XONIZATION DETECTOR ASSEMBLY This invention relates to flameionization detectors, and more particularly-to flame ionizationdetectors suitable for use in separations by gas chromatography.

The detection of variations with time of the composition of the gaseouseffluent from a chromatography column lead to a flame by detection ofvarious peaks by means of ionization measurement of the flame is wellknown. In chromatography for purely analytical purposes, the flow ofgaseous effluent is quite low, and thus the entire flow can be fed tothe detector in which separation of the peaks can be achieved withoutthe occurrence of streaks or overlapping.

However, in applications of gas chromatography in which gaseous effluentfrom the column is continuously subjected to analysis, sometimesreferred to as preparative chromatography, the greater portion of thegaseous effluent is intended to be collected in the form of separatedportions. For this purpose, apparatus heretofore employed have includedvarious branch tubing in the outlet piping of the chromatographiccolumn, flow control valves and connections to the flame detector, allof which contribute to a number of problems as a result of branch tubingprocesses and large dead volumes in the apparatus.'

The primary difficulties incurred through the use of apparatus of thetype described involve a decrease in the acuteness or sharpness of thepeaks detected by the ionization detector and the occurrence ofdisturbances in the gaseous effluent flow from the chromatographycolumn, whereby the selectivity of the chromatographic apparatus issignificantly decreased. in addition, because of the large dead volumeof the apparatus, the variations in the composition of the main streamof the effluent flow from the column do not correspond to the imagegiven by the detector, thereby making it impossible to efficientlyprogram the separation of the various fractions.

it is accordingly an object of the present invention to provide a flameionization detector which is capable of overcoming the foregoingdisadvantages.

It is a more specific object of the invention to provide a flameionization detector suitable for use with chromatographic separationshaving a minimum of dead volume so as to be capable of detecting sharppeaks without the occurrence of disturbances caused by too large adiversion of the primary gas flow.

These and other objects and advantages of the invention will appearhereinafter, and, for purposes of illustration, but not of limitation,an embodiment of the invention is shown in the attached drawing in whichthe figure represents a cross section of a flame ionization detectorembodying the features of the invention.

The concepts of the present invention reside in a detector assemblyincluding a gas sampling assembly for use with a detector comprising ahousing defining primary passage means for the gaseous effluent from thechromatography column, passage means for a fraction of the flow ofcolumn effluent, and a valve to control the flow of this fraction to thedetector. This assembly can be used in conjunction with a conventionaldetector including a burner head, measuring electrodes, temperaturemeasuring means, an ignitor and a protective bell to provide a flameionization detector having a minimum of dead volume which is capable ofdetecting sharp peaks without the occurrence of disturbances caused bytoo large a diversion in the primary gas flow.

In the preferred form of the invention, the housing is in the form of asolid block, preferably formed of a metal, which defines the passagemeans therethrough as well as the recess for the glass flow controlvalve and the passages for the electrodes and other detector elements.

Refering now to the drawing, there is shown a device embodying thefeatures of the invention including a block 1 forming the housing. Thehousing block 1 is preferably formed of a metal, such as stainlesssteel, and defines a passage 2 through which the primary gas flow fromthe column can exit from the device. The gaseous influent to theapparatus of the invention is fed to passage defined in flange 4 andannular element 3. Passage 25 communicates with passage 2 so as todefine a primary tube or passage through which the primary gas flow fromthe column may pass.

Housing block 1 also defines a recess adapted to receive a valve seatmember 6 having a passage 7 having a small diameter therethroughcommunicating with the primary tube defined by passages 25 and 2 whichis maintained in its recess by means of the abutting relationship ofannular element 3. The valve seat member 3 is preferably formed of aplastic material which is stable against chemical attack from thegaseous effluent of the column and thermally stable at the prevailingcolumn effluent material. For this purpose, use is preferably made of avalve seat member formed of polytetrafluorethylene, although use canalso be made of a variety of other materials.

Housing block 1 also defines a recess adapted to receive a coaxialneedle 9 which extends through the recess, and is adapted to seat invalve seat element 6. As shown in the drawing, valve seat element 6 hasa conical recess defined by surface 8 which is adapted to receive thecorresponding conical end of needle 9 in a sealing relationship when thevalve is closed. The upper end of needle 9 is threadably engaged withhousing block 1 by means of thread means 12, and needle 9 is adapted tobe displaced into sealing engagement with valve seat 6 by means of agear wheel 17 fixed to needle 9 by way of block 13 which is actuated byan endless screw 18 which extends through housing 1 where it isaccessible on the outside thereof to rotate needle 9 about itscylindrical axis and thereby displace needle 9 relative to valve seatmember 6.

Near its lower portion, needle 9 is sealed from its recess by means oftoroidal sealing means 10 whereby the conical surface of needle 9 andthe corresponding conical recess of surface 8 of seat element 6 define aspace therebetween when the valve is at least partially open. As shownin the figure, the space defined by needle 9 and surface 8 communicateson the one hand with passage 7 extending through seat member 6. Thespace also communicates with passages 11 and 16 extending at leastpartially through needle 9 whereby gases are perknitted to flow throughpassage means 7 to the space defined by needle 9 and surface 8 andthrough passage means 11 and 16 to combustion chamber 26 defined byhousing I. Since passage 16 extends into combustion chamber 26, tube 16is preferably formed'of a refractory material such as fused silica orthe like extending through a bushing 15 formed of a plastic material,such as polytetrafiuoroethylene. As shown in this figure, the lowerpostion of passage 11 is oblique relative to the axis of needle 9 andextends substantially perpendicular to the conical surface of needle 9and to surface 8. However, a variety of other positions of the lowerportion of passage means 11 are similarly suitable in the invention tofeed a small amount of the effluent to the combustion zone.

Housing 1 also defines a passage 19 for the introduction of a fuel gas,preferably hydrogen, to combustion chamber 26 by means of tube 20extending through a plastic bushing 21. Similarly, housing 1 definespassage means 22 for the introduction of an oxygen-containing gas suchas air to combustion zone 26. While it is not illustrated in thedrawing, the top of combustion zone 26 may be provided with a protectivebell of the type conventionally used in flame ionization detectors,which may be threadably engaged with threads 23 and sealed by sealingmeans 24. Also not illustrated in the drawing for the sake of simplicityare the standard elements of a flame ionization detector including themeasuring electrodes, temperature measuring means, such as athermocouple, and an electrical resistance ignitor.

In use, the gaseous effluent from a chromatography column is fed to theprimary tube defined by passages 25 and 2 whereby the gases flowtherethrough. The needle valve is opened by causing shaft 18 to rotate,thereby turning wheel 17 and displacing needle 9 upwardly away fromvalve seat member 6 to define a space between needle 9 and surface 8 ofvalve seat member 6. This enables a small portion of the gas passingthrough passage 25 to pass through passage 7 in valve seat member 6 andthrough passage 11 in needle 9 and through tube 16 where the gas iscontacted with a hydrogenoxygen flame in combustion zone 26. Ionizationof the gas in the flame can then be measured by means of the electrodesin a conventional manner.

It will be apparent from the foregoing that the device of the presentinvention has a very small dead volume since it makes use of passagemeans having a small diameter and short length joining the primary gasflow and the flame. The quantity of gas samples can easily be regulatedby displacement of needle 9 relative to valve seat member 6. However, itwill be understood by those skilled in the art that the various elementsare not restricted to the configurations illustrated in the drawing. Forexample, the tube for primary gas flow may be rectilinear or have aregular curvature instead of the right angle tube illustrated. Inaddition, it is possible to provide a tube having a small diameterextending into passage 2, preferably so as to be coaxial therewith,whereby a fraction of the column effluent may flow through this tube topassage 7 and to combustion zone 26.

It will be understood that various modifications and changes can be madein the details of construction and use without departing from the spiritof the invention, especially as defined in the following claims.

We claim:

1. In a flame ionization detector assembly for use in gas chromatographyin which a small portion of the effluent from a chromatography column ispassed to a combustion zone for flame ionization, the improvementcomprising a housing, said housing defining first passage means forgaseous effluent from a chromatography column, a needle and valve seatmeans, both of which are adapted to be received in recesses defined bysaid housing with the needle being mo'veable relative to the valve seatmeans to define a space therebetween when the needle is moved away fromthe valve seat means to an open position, said valve seat meansincluding a small passage communicating with the first passage and saidneedle including an internal passage communicating with the combustionzone and the space defined between the needle and the valve seat means,whereby a small portion of gas passes from the first passage through thesmall passage of the valve seat means and the internal passage of theneedle to the combustion zone, and passage means to supply anoxygen-containing gas and a fuel gas to the combustion zone.

2. An assembly as defined in claim 1 wherein said housing is in the formof a block.

3. An assembly as defined in claim 2 wherein said block is formed ofmetal.

4. An assembly as defined in claim 2 wherein said block is formed ofstainless steel.

5. An assembly as defined in claim 1 wherein said valve seat means has aconical recess formed therein and said needle has a conical section onone end thereof, said conical recess being adapted to receive saidconical section of said needle in sealing relation when said needle isin closed position.

6. An assembly as defined in claim 1 wherein said valve seat means isformed of a plastic.

7. an assembly as defined in claim 1 wherein said needle is threadablyreceived in said recess in said housing, said needle being moveable inresponse to rotation in threaded engagement in said housing.

8. An assembly as defined in claim 7 which includes a gear wheel fixedto said needle and an endless screw engaged with said gear wheel, saidneedle being rotatable in response to rotation of said screw.

9. An assembly as defined in claim 1 wherein a portion of the internalpassage defined by said needle is coaxial therewith.

10. An assembly as defined in claim 9 wherein the remaining portion ofthe internal passage defined by said needle is oblique with res ect tothe axis of said needle.

11. An assem ly as defined in claim 1 wherein said passage means tosupply fuel are defined by said housing.

12. An assembly as defined in claim 1 wherein said first passage meansis formed by right angle passages.

13. An assembly as defined in claim 1 wherein said first passage meansof rectilinear.

14. An assembly as defined in claim 1 wherein said first passage meansis curved.

15. An assembly as defined in claim I wherein said assembly includes adetector including measuring electrodes, temperature measuring means andignitor.

2. An assembly as defined in claim 1 wherein said housing is in the formof a block.
 3. An assembly as defined in claim 2 wherein said block isformed of metal.
 4. An assembly as defined in claim 2 wherein said blockis formed of stainless steel.
 5. An assembly as defined in claim 1wherein said valve seat means has a conical recess formed therein andsaid needle has a conical section on one end thereof, said conicalrecess being adapted to receive said conical section of said needle insealing relation when said needle is in closed position.
 6. An assemblyas defined in claim 1 wherein said valve seat means is formed of aplastic.
 7. an assembly as defined in claim 1 wherein said needle isthreadably received in said recess in said housing, said needle beingmoveable in response to rotation in threaded engagement in said housing.8. An assembly as defined in claim 7 which includes a gear wheel fixedto said needle and an endless screw engaged with said gear wheel, saidneedle being rotatable in response to rotation of said screw.
 9. Anassembly as defined in claim 1 wherein a portion of the internal passagedefined by said needle is coaxial therewith.
 10. An assembly as definedin claim 9 wherein the remaining portion of the internal passage definedby said needle is oblique with respect to the axis of said needle. 11.An assembly as defined in claim 1 wherein said passage means to supplyfuel are defined by said housing.
 12. An assembly as defined in claim 1wherein said first passage means is formed by right angle passages. 13.An assembly as defined in claim 1 wherein said first passage means ofrectilinear.
 14. An assembly as defined in claim 1 wherein said firstpassage means is curved.
 15. An assembly as defined in claim 1 whereinsaid assembly includes a detector including measuring electrodes,temperature measuring means and ignitor.